Conventional brushless direct current (DC) motors rely on the magnetic flux created by permanent magnets located on the rotor interacting with magnetic fields from the stator to generate a mechanical torque. Indeed, the output mechanical torque generated by a brushless DC motor is directly proportional to the magnetic flux density of the rotor magnets. Often, performance characteristics of a brushless DC motor are evaluated based on the output mechanical torque generated by the motor as a function of the input stator current. In many applications, it is critical to accurately determine the output mechanical torque produced by a motor for a known stator current.
The magnetic flux of the rotor magnets and its relationship with the magnetic fields induced by the stator current is a function of the motor temperature. It is well known that the magnetic flux density of magnetic materials (i.e., rotor magnets) decreases as temperature increases, resulting in degradation of motor performance. Herethereto, conventional approaches to this problem have been to simply recognize a performance degradation during high-temperature operation and attempt to try to regulate the ambient temperature, or to recommend only certain operating temperature conditions.
It would therefore be desirable to provide systems and methods for accurately sensing the temperature of the rotor magnets to provide more accurate output torque information.